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 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/

/**
 *  \brief HAVEGE: HArdware Volatile Entropy Gathering and Expansion
 *
 *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *  This file is part of mbed TLS (https://tls.mbed.org)
 */
/*
 *  The HAVEGE RNG was designed by Andre Seznec in 2002.
 *
 *  http://www.irisa.fr/caps/projects/hipsor/publi.php
 *
 *  Contact: seznec(at)irisa_dot_fr - orocheco(at)irisa_dot_fr
 */

#include "tls/config.h"

#if defined(MBEDTLS_HAVEGE_C)

#include "tls/havege.h"
#include "tls/timing.h"

#include <string.h>

/* Implementation that should never be optimized out by the compiler */
static void mbedtls_zeroize(void *v, size_t n)
{
	volatile unsigned char *p = v;
	while (n--) {
		*p++ = 0;
	}
}

/* ------------------------------------------------------------------------
 * On average, one iteration accesses two 8-word blocks in the havege WALK
 * table, and generates 16 words in the RES array.
 *
 * The data read in the WALK table is updated and permuted after each use.
 * The result of the hardware clock counter read is used  for this update.
 *
 * 25 conditional tests are present.  The conditional tests are grouped in
 * two nested  groups of 12 conditional tests and 1 test that controls the
 * permutation; on average, there should be 6 tests executed and 3 of them
 * should be mispredicted.
 * ------------------------------------------------------------------------
 */

#define SWAP(X, Y) { int *T = X; X = Y; Y = T; }

#define TST1_ENTER if (PTEST & 1) { PTEST ^= 3; PTEST >>= 1;
#define TST2_ENTER if (PTEST & 1) { PTEST ^= 3; PTEST >>= 1;

#define TST1_LEAVE U1++; }
#define TST2_LEAVE U2++; }

#define ONE_ITERATION                                   \
														\
	PTEST = PT1 >> 20;                                  \
														\
	TST1_ENTER  TST1_ENTER  TST1_ENTER  TST1_ENTER      \
	TST1_ENTER  TST1_ENTER  TST1_ENTER  TST1_ENTER      \
	TST1_ENTER  TST1_ENTER  TST1_ENTER  TST1_ENTER      \
														\
	TST1_LEAVE  TST1_LEAVE  TST1_LEAVE  TST1_LEAVE      \
	TST1_LEAVE  TST1_LEAVE  TST1_LEAVE  TST1_LEAVE      \
	TST1_LEAVE  TST1_LEAVE  TST1_LEAVE  TST1_LEAVE      \
														\
	PTX = (PT1 >> 18) & 7;                              \
	PT1 &= 0x1FFF;                                      \
	PT2 &= 0x1FFF;                                      \
	CLK = (int) mbedtls_timing_hardclock();                            \
														\
	i = 0;                                              \
	A = &WALK[PT1]; RES[i++] ^= *A;                 \
	B = &WALK[PT2]; RES[i++] ^= *B;                 \
	C = &WALK[PT1 ^ 1]; RES[i++] ^= *C;                 \
	D = &WALK[PT2 ^ 4]; RES[i++] ^= *D;                 \
														\
	IN = (*A >> (1)) ^ (*A << (31)) ^ CLK;              \
	*A = (*B >> (2)) ^ (*B << (30)) ^ CLK;              \
	*B = IN ^ U1;                                       \
	*C = (*C >> (3)) ^ (*C << (29)) ^ CLK;              \
	*D = (*D >> (4)) ^ (*D << (28)) ^ CLK;              \
														\
	A = &WALK[PT1 ^ 2]; RES[i++] ^= *A;                 \
	B = &WALK[PT2 ^ 2]; RES[i++] ^= *B;                 \
	C = &WALK[PT1 ^ 3]; RES[i++] ^= *C;                 \
	D = &WALK[PT2 ^ 6]; RES[i++] ^= *D;                 \
														\
	if (PTEST & 1) SWAP(A, C);                       \
														\
	IN = (*A >> (5)) ^ (*A << (27)) ^ CLK;              \
	*A = (*B >> (6)) ^ (*B << (26)) ^ CLK;              \
	*B = IN; CLK = (int) mbedtls_timing_hardclock();                   \
	*C = (*C >> (7)) ^ (*C << (25)) ^ CLK;              \
	*D = (*D >> (8)) ^ (*D << (24)) ^ CLK;              \
														\
	A = &WALK[PT1 ^ 4];                                 \
	B = &WALK[PT2 ^ 1];                                 \
														\
	PTEST = PT2 >> 1;                                   \
														\
	PT2 = (RES[(i - 8) ^ PTY] ^ WALK[PT2 ^ PTY ^ 7]);   \
	PT2 = ((PT2 & 0x1FFF) & (~8)) ^ ((PT1 ^ 8) & 0x8);  \
	PTY = (PT2 >> 10) & 7;                              \
														\
	TST2_ENTER  TST2_ENTER  TST2_ENTER  TST2_ENTER      \
	TST2_ENTER  TST2_ENTER  TST2_ENTER  TST2_ENTER      \
	TST2_ENTER  TST2_ENTER  TST2_ENTER  TST2_ENTER      \
														\
	TST2_LEAVE  TST2_LEAVE  TST2_LEAVE  TST2_LEAVE      \
	TST2_LEAVE  TST2_LEAVE  TST2_LEAVE  TST2_LEAVE      \
	TST2_LEAVE  TST2_LEAVE  TST2_LEAVE  TST2_LEAVE      \
														\
	C = &WALK[PT1 ^ 5];                                 \
	D = &WALK[PT2 ^ 5];                                 \
														\
	RES[i++] ^= *A;                                     \
	RES[i++] ^= *B;                                     \
	RES[i++] ^= *C;                                     \
	RES[i++] ^= *D;                                     \
														\
	IN = (*A >> (9)) ^ (*A << (23)) ^ CLK;             \
	*A = (*B >> (10)) ^ (*B << (22)) ^ CLK;             \
	*B = IN ^ U2;                                       \
	*C = (*C >> (11)) ^ (*C << (21)) ^ CLK;             \
	*D = (*D >> (12)) ^ (*D << (20)) ^ CLK;             \
														\
	A = &WALK[PT1 ^ 6]; RES[i++] ^= *A;                 \
	B = &WALK[PT2 ^ 3]; RES[i++] ^= *B;                 \
	C = &WALK[PT1 ^ 7]; RES[i++] ^= *C;                 \
	D = &WALK[PT2 ^ 7]; RES[i++] ^= *D;                 \
														\
	IN = (*A >> (13)) ^ (*A << (19)) ^ CLK;             \
	*A = (*B >> (14)) ^ (*B << (18)) ^ CLK;             \
	*B = IN;                                            \
	*C = (*C >> (15)) ^ (*C << (17)) ^ CLK;             \
	*D = (*D >> (16)) ^ (*D << (16)) ^ CLK;             \
														\
	PT1 = (RES[(i - 8) ^ PTX] ^                      \
			WALK[PT1 ^ PTX ^ 7]) & (~1);               \
	PT1 ^= (PT2 ^ 0x10) & 0x10;                         \
														\
	for	(n++, i = 0; i < 16; i++)                      \
		hs->pool[n % MBEDTLS_HAVEGE_COLLECT_SIZE] ^= RES[i];

/*
 * Entropy gathering function
 */
static void havege_fill(mbedtls_havege_state *hs)
{
	int i, n = 0;
	int U1, U2, *A, *B, *C, *D;
	int PT1, PT2, *WALK, RES[16];
	int PTX, PTY, CLK, PTEST, IN;

	WALK = hs->WALK;
	PT1 = hs->PT1;
	PT2 = hs->PT2;

	PTX = U1 = 0;
	PTY = U2 = 0;

	(void)PTX;

	memset(RES, 0, sizeof(RES));

	while (n < MBEDTLS_HAVEGE_COLLECT_SIZE * 4) {
		ONE_ITERATION ONE_ITERATION ONE_ITERATION ONE_ITERATION
	}
	hs->PT1 = PT1;
	hs->PT2 = PT2;

	hs->offset[0] = 0;
	hs->offset[1] = MBEDTLS_HAVEGE_COLLECT_SIZE / 2;
}

/*
 * HAVEGE initialization
 */
void mbedtls_havege_init(mbedtls_havege_state *hs)
{
	memset(hs, 0, sizeof(mbedtls_havege_state));

	havege_fill(hs);
}

void mbedtls_havege_free(mbedtls_havege_state *hs)
{
	if (hs == NULL) {
		return;
	}

	mbedtls_zeroize(hs, sizeof(mbedtls_havege_state));
}

/*
 * HAVEGE rand function
 */
int mbedtls_havege_random(void *p_rng, unsigned char *buf, size_t len)
{
	int val;
	size_t use_len;
	mbedtls_havege_state *hs = (mbedtls_havege_state *) p_rng;
	unsigned char *p = buf;

	while (len > 0) {
		use_len = len;
		if (use_len > sizeof(int)) {
			use_len = sizeof(int);
		}

		if (hs->offset[1] >= MBEDTLS_HAVEGE_COLLECT_SIZE) {
			havege_fill(hs);
		}

		val = hs->pool[hs->offset[0]++];
		val ^= hs->pool[hs->offset[1]++];

		memcpy(p, &val, use_len);

		len -= use_len;
		p += use_len;
	}

	return (0);
}

#endif							/* MBEDTLS_HAVEGE_C */
